Lovely Runner

Both FLs time travel into the past and their school days in order to save the ML who appears to have committed suicide.

A male lead who can't confess to his first love. He travels back in time and returns to his high school years. This time he tries to help the girl he loves to confess to her past self..................................................

Both FLs time travel back to their school days.
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ML likes FL first (this one actively chases after her tho) but both really REALLY like her.
Suburban/Small town setting
Same quirky humor
Serial killer after the female lead
Both these shows add some aspects of a thriller in the drama which juxtaposes the bright romantic tone the show presents itself as.
(Both shows are able to still stay light throughout it tho)

Both dramas are about one of the leads suddenly dying and the other time traveling back to their school days in an effort to save their life.

Both dramas include travelling to the past to change the future with back and forth travel and unravelling more details as you go along.

Both also travel back to the high school days.

However, Lovely Runner features on the FL travelling through time, while A Chan features both ML and FL travelling back and forth -and- with a soul swap to boot!

Both dramas are about one of the leads suddenly dying and the other time traveling back to the past in an effort to save their life.

- FL thought she fell first, but it’s the ML who liked her first!
- Good chemistry between the leads

Both FLs time travel to their school days in an effort to save someone.
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Both dramas are about one of the leads suddenly dying and the other attempting through time travel to save their life.

Both FLs time travel into the past to save the ML who has died in the present. It's then revealed that the ML was secretly in love with her a long time before she believes they first met.

In both series, he saves the life of one of the characters by time travel.
They have crime, romance and humor.
The character has to go back in time several times.
It takes place in modern times.
A handsome man and a cheerful, lovely girl.

I know these have nothing to do with each other in a sense, but the "time travel" aspect kind of gave me this sense of, if you make the wrong decision someone you love could die. Lovely Runner of course is not a BL, but I found the ending to be more satisfying than 4M.
Also LR has some what if moments to it, while also being a thriller. Not as cinematographic as 4M, but has some comedic moments to make up for that.

Shining for one thing: The movie is a movie while Lovely Runner is a show.
FL travels back in time to save ML.
ML had feelings for the FL from the beginning.
A tragic accident took ML's life.
Everything begins in the school.
Friends turned lovers.

In the glitzy realm of stardom, Ryu Seon Jae shines as a top-tier celebrity, captivating the spotlight since his debut. Despite the facade of a perfect life, the demanding nature of the entertainment industry has left him utterly exhausted. Im Sol, an ardent admirer, holds an affectionate love for Ryu Seon Jae. A childhood accident derailed her dreams, yet the solace found in Ryu Seon Jae's music on the radio transformed her into an unwavering fan. The narrative takes a poignant turn when Im Sol, reeling from the breaking news of Ryu Seon Jae's tragic demise, experiences a miraculous twist of fate. Transported back 15 years into the past, she confronts Ryu Seon Jae in his 19-year-old high school self. Im Sol grapples with the formidable challenge of altering the trajectory of his future, driven by an unyielding determination to avert the impending tragedy.